In many heavy duty vehicles, such as farm and industrial equipment, most of the electrical requirements are satisfied by a standard twelve-volt output. The starting system in such vehicles and sometimes other electrical equipment often require a 24-volt output.
In order to provide the higher voltage for the starter and other components which may require it, it is not unusual for vehicles to have an electrical system incorporating two sets of batteries connected in series. In such configurations, most of the electrical circuitry is connected across one of the batteries, the primary battery, while the starter system and any other higher voltage components are connected across both batteries, the primary battery and the secondary battery.
In vehicles, of course, it is necessary to maintain the batteries charged. This is usually accomplished by a regulated alternator connected across the battery. Such alternators are not inexpensive because typically they include not only the alternator itself but also the necessary rectification, temperature control, and voltage regulation for the alternator output.
The standard alternator is designed for use with a twelve-volt vehicular electrical system. Such alternators, of course, do not function to regulate a 24-volt output which exists in dual voltage systems described above. It is clear, therefore, that some means must be provided to establish the necessary regulated output for such a plural voltage system.
It would, of course, be possible to utilize a pair of twelve-volt alternator assemblies, one across each battery. This is not necessarily a satisfactory solution because of the added expense of the second alternator. As a result, it has been proposed to incorporate some type of voltage multiplier circuit for producing an increased output voltage. Typically, the voltage multiplier is a doubler producing a nominally 24-volt output from the nominally twelve-volt output of the regulated alternator.
Such doubler circuits, for example, are disclosed in Lovrenich U.S. Pat. No. 3,206,610, Campbell et al. U.S. Pat. No. 3,624,480, and Pfeffer et al U.S. Pat. No. 4,100,474.
The problem with such voltage doubler circuits is that the supposedly doubled output voltage is not necessarily the double of the original twelve-volt output of the regulated alternator. Furthermore, there is no regulation or at best inadequate regulation of the 24-volt output. The only regulation results from the fact that the input to the doubler is the regulated twelve-volt output of the alternator.
In the multi-voltage system disclosed in Pfeffer, the input for the voltage double is taken in part from one of the windings of the three-phase alternator. Unfortunately, not all alternators provide access to such a winding. In addition, if the load on that single winding is large, as it may be to operate the starter or to charge the secondary battery, the alternator becomes unbalanced which in itself could create a variety of problems as is well-known.
The doubler circuit in Pfeffer is not itself regulated. It merely relies on the existence of a regulated input thereto, i.e., the output of the alternator. Therefore, the charging voltage and current for the secondary battery are not truly regulated nor are they necessarily maintained at proper values.
It would be desirable, therefore, to be able to produce regulated plural output voltages of selected values from a regulated source, which could be usable with a variety of existing type alternators and which would not require any special connection thereto, which would be relatively inexpensive, particularly as compared to a second alternator assembly, and which would provide the desired regulated plural outputs.